The present invention relates to an array disk apparatus wherein serial data is dividedly stored into a plurality of disk units from which the divided data is read and composed into the original serial data.
Recent developments in computer technology are phenomenal. Particularly impressive is the enhanced speed of processing by the CPU (central processing unit). The information processed by computer is generally stored in external storage devices. As information is processed by computer at speeds higher than ever before, there is a growing need for magnetic disk units that function as external storage devices to and from which information is stored and retrieved at correspondingly higher speeds. Although magnetic disk units working as external storage devices have relatively short access times, they are incapable of fully addressing the accelerated rates at which CPUs process their data. It is to fill the speed discrepancy between storage and processing that what is known as the array magnetic disk apparatus has been developed. A typical conventional magnetic disk apparatus uses a plurality of magnetic disk units (e.g., 8 units) to which data is dividedly stored. For data retrieval, the divided data is read from the multiple magnetic disk units and composed into the original data.
A conventional array disk apparatus comprises a plurality of magnetic disk units to which data is dividedly stored, a parity data magnetic disk unit to which the parity data associated with the dividedly stored data is stored, and a disk controller. The disk controller contains a data reconstructing unit that reconstructs data in a magnetic disk unit to and from which data cannot be written or read for some error, the reconstruction being carried out after repair of the error based on the data from the other magnetic disk units and from the parity data magnetic disk unit.
The array magnetic disk apparatus of the above construction divides data (e.g., 0, 1, 2, 3, . . . , N, 2N, . . .) into "n" (e.g., 8) pieces for storage into "n" magnetic disk units. The disk controller of the apparatus has its parity data generating unit which generates parity data "P1, P2 . . . , Pn . . ." for the divided data and places the parity data into the parity data magnetic disk unit. For data retrieval, the divided data is read simultaneously from the magnetic disk units and the associated parity data is read from the parity data magnetic disk unit. The retrieved data is reconstructed by the data reconstructing unit for output as serial data. If one magnetic disk unit develops an error and part or all of the data stored therein cannot be read therefrom, the data from the remaining magnetic disk units and the parity data from the parity data magnetic disk unit are used to reconstruct the affected data to be stored in the failed magnetic disk unit after the repair thereof.
One disadvantage of the above conventional array disk apparatus is that if another magnetic disk unit develops a read error while the repaired unit has its data being reconstructed, it is impossible to reconstruct data to be stored in the failed and repaired unit. In that case, the conventional array disk apparatus must be stopped halfway in its data reconstruction process and some appropriate action must be taken.